Infinite Looping code and jstack

[Scott Oaks]

We have an appserver installation where some set of threads get into an
infinite loop. jstack always reports that the threads in question are at
a specific line.

Here's a snippet of the jstack output:
"http80-Processor584" daemon prio=10 tid=0x015af400 nid=0x8d4 runnable
[0x26bdf000..0x26bdf9f0]
   java.lang.Thread.State: RUNNABLE
        at
org.apache.coyote.http11.InternalInputBuffer.parseHeader(InternalInputBuffer.java:805)
        at
org.apache.coyote.http11.InternalInputBuffer.parseHeaders(InternalInputBuffer.java:607)
        at
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:667)

parseHeader (line 805) isn't really a loop at all; there's no way I can
account for the infinite loop being in that method. It's conceivable
somehow that parseHeaders (line 607) could be in a loop:

    while (parseHeader())
          doSomething

But in that case, wouldn't I get somewhat differing results from
successive invocations jstack (or even one jstack where multiple threads
are in the same method)? 

I guess what I'm really asking is what the granularity of jstack is --
if I were in an infinite loop over two methods and 40-50 lines of code,
is it really conceivable that jstack would always show me I was on the
very same line (because that line corresponds to a safepoint or
something)? Or is something else more likely going on?

This is with JDK 1.6.0_02 and the server compiler.

-Scott